Eternal Fourth Protection (久遠第四加護, Kuon daiyon kago) or Kú Li Anse (クー・リ・アンセ, Kū Ri anse) is a spell developed by Think Nirvalen. It was once used by Jibril in Materialization Shiritori. It creates a magical barrier around the users target and protects them from harm. It is stated to be the highest level sealing spell and even protected Sora and Shiro from a point blank hydrogen bomb.
Eternal Fourth Protections, commonly known as Bkulians, is a high-level sealing spell that requires connection to the Spirit Circuits to complete. It seals everything in a complete sphere, even the soil beneath it.
In the past, Jibril fired a Heavenly Smite on the Elven capital, where a rite of protection deployed by 3000 elves had failed to block the attack. In light of this, Think Nirvalen composed a greater rite of sealing. Deployed under the protection of Old Deus Kainas, the spell is strong enough to block a Heavenly Smite (but not against a Godly Smite).
It is stated in Volume 6, during the Great War, that the Eternal Fourth Protection was a spell developed by Think Nirvalen after it's knowledge was lost to the Flügel.